MX2012003172A

MX2012003172A - Method for removal of carbon dioxide from a process gas.

Info

Publication number: MX2012003172A
Application number: MX2012003172A
Authority: MX
Inventors: Arlyn V Petig; Frederic Z Kozak
Original assignee: Alstom Technology Ltd
Priority date: 2009-09-15
Filing date: 2010-09-01
Publication date: 2012-06-12
Also published as: AU2010295886B2; AU2010295885B2; JP2013504423A; CN102596364B; BR112012005813A2; MA33664B1; ZA201202700B; IN2012DN03069A; KR20120066655A; KR20120066038A; KR20120066657A; AU2010295884A1; WO2011034726A1; CA2774188A1; CA2774201A1; US20110061533A1; EP2477722A1; MX2012003173A; CN102596365A; AU2016203360A1

Abstract

The invention relates to a method of removing carbon dioxide from a process gas, the method comprising: a) allowing an ammoniated solution to enter an absorption arrangement, said absorption arrangement comprising at least a first absorber; b) contacting the ammoniated solution with the process gas in said first absorber, the ammoniated solution capturing at least a part of the carbon dioxide of the process gas; c) allowing the ammoniated solution to exit the absorption arrangement; d) cooling the ammoniated solution, wherein at least a part of the captured carbon dioxide is precipitated as solid salt; e) allowing the cooled ammoniated solution to enter a separator, in which separator at least a part of the precipitated solids are removed from the ammoniated solution, after which the ammoniated solution is allowed to exit the separator; f) heating the ammoniated solution; and g) allowing the heated ammoniated solution to re-enter the absorption arrangement. The invention also relates to a carbon dioxide removal system.

Description

METHOD FOR ELIMINATING CARBON BIOXIDE FROM A PROCESS GAS TECHNICAL FIELD The present invention relates to a method for removing carbon dioxide from a process gas by contacting the process gas with an ammonia solution.

BACKGROUND Most of the energy used in the world today derives from the combustion of fuels that contain carbon and hydrogen such as coal, oil, and natural gas, as well as other organic fuels. This combustion generates combustion gases that contain high levels of carbon dioxide. Due to concerns about global warming, there is a demand that is increased by the reduction of emissions of carbon dioxide to the atmosphere, so that methods have been developed to remove carbon dioxide from the combustion gases before releasing the gas to the atmosphere.

WO 2006/022885 discloses one of those methods for removing carbon dioxide from a combustion gas, said method includes capturing carbon dioxide from the combustion gas in an absorbent, of C02 by means of an ammonia solution or sludge. The C02 is absorbed by the ammoniacal solution in the absorber at a reduced temperature between approximately 0 ° C and 20 ° C, after which the ammoniacal solution is regenerated in a regenerator under high pressure and temperature to allow the C02 to escape from the ammoniacal solution as high purity gaseous carbon dioxide.

COMPENDIUM An objective of the present invention is to improve the absorption method of carbon dioxide with an ammoniacal solution.

This objective, as well as other objectives that will be clear from the following discussion, in accordance with an aspect achieved by a method of removing carbon dioxide from a process gas, the method comprises: a) allowing an ammonia solution to be introduce an absorption assembly, said absorption configuration comprises at least a first absorbent; b) contacting the ammonia solution with the process gas in said first, absorbent, ammoniacal solution captures at least a part of the carbon dioxide from the process gas; c) allow the ammoniacal solution to exit the absorption assembly; d) cooling the ammonia solution, wherein at least a part of the captured carbon dioxide is precipitated as a solid salt; e) allowing the cooled ammoniacal solution to enter a separator, in which separator at least a portion of the precipitated solids are removed from the ammoniacal solution, after which the ammoniacal solution is allowed to exit the separator; f) heating the ammonia solution; and g) allowing the heated ammoniacal solution to re-enter the absorption assembly.

The absorption assembly may comprise one or more absorbents. In its simplest design, the absorption assembly may comprise a single absorbent. This simple design can also simplify the method of removing carbon dioxide and will reduce the costs of assembly maintenance. The absorber (s) can be of any design that allows direct contact to be made between the ammonia solution and the process gas within the absorbent.

When the ammoniacal solution is contacted with the process gas, the carbon dioxide can be removed from the process gas and captured by the ammoniacal solution when crossing the inferium formed between the process gas and the ammoniacal solution.

There is a limit to how much carbon dioxide the ammoniacal solution can capture, that is, when the ammoniacal solution reaches saturation. This limit depends, for example, on the pressure and temperature of the solution. Upon cooling the ammonia solution, the ability of the solution to dissolve the carbon dioxide is reduced, so that at least a part of the captured carbon dioxide is precipitated as a solid salt. Even if the ammoniacal solution has not reached saturation in the absorption assembly and solids have not been precipitated before cooling the solution, the cooling of the ammoniacal solution in d) allows the precipitation of captured carbon dioxide in the form of a salt solid Therefore, at least part of the captured carbon dioxide can be separated from the ammoniacal solution by the separator by removing at least a portion of the precipitated solids.

The ammonia solution leaving the separator may be saturated with carbon dioxide since the separator can only remove carbon dioxide in precipitated solid form. By heating the ammonia solution in f), the ability of the solution to dissolve carbon dioxide increases, allowing the ammoniacal solution to return to the absorption assembly to capture more carbon dioxide without precipitation of solids.

By cooling the ammonia solution, removing the solids, and reheating the solution, most of the ammonia solution can return to the absorption assembly to capture more carbon dioxide without precipitation of solids. Therefore, there is no need to regenerate the full solution stream. Instead, the much smaller volume of solids, and optionally a little solution, removed by the separator and having a much higher concentration of carbon dioxide can be transferred to a regenerator. Since the regenerator applies increased pressure and temperature to the solution, slurry or sludge that is regenerated in order to obtain high purity carbon dioxide, the energy consumption is greatly reduced if the volume of the solution, suspension or sludge is reduced and the concentration of carbon dioxide increases.

Also, by inducing precipitation of solids by cooling the solution Ammoniacal, carbon dioxide in the solid salt form can be removed from the ammoniacal solution although the ammoniacal solution leaving the absorption assembly does not contain precipitated solids, that is, the ammoniacal solution leaving the absorption assembly can be rich in dioxide. carbon but not completely saturated or supersaturated and still allow the elimination of carbon dioxide in solid form by the separator. This implies that the precipitation of solids within the absorption assembly and the absorber can be reduced or even stopped completely compared to if no cooling had been carried out. Precipitation of solids can be undesirable since solids can clog pipes, valves, pumps, absorbers etc., and can also increase the wear of the absorption assembly due to increased abrasion by the flow of ammonia solution. If there is no precipitation, or it is reduced only in the absorption assembly, the absorption assembly may not have to be designed to contain solid particles in the ammonia solution, so the absorption assembly can be designed in a simpler way and for a more efficient capture of carbon dioxide, for example by a more effective packaging material in the absorbent if a packaging material is used, which packaging material could otherwise clog and result in excessive pressure drop. Also, the maintenance of the absorption assembly could be greatly reduced.

It may be convenient to control the temperature of the ammonia solution while it comes in contact with the process gas in the first absorber, as well as the temperature of the first absorber, that is, the temperature at which the carbon dioxide is captured by the ammoniacal solution. , it could be controlled. While the temperature is reduced, the rate at which the carbon dioxide is captured from the process gas by the ammonia solution is also reduced. If the temperature increases, the rate at which the gaseous ammonia exits and depletes the ammoniacal solution also increases. The temperature of the absorber is therefore a compensation between the rate of uptake and the depletion of ammonia. It has been found that a temperature of the ammonia solution while contacting the process gas in the first absorbent of between about 10 ° C and 20 ° C (50 ° F and 68 ° F) may be convenient, especially a temperature of about 15 ° C (59 ° F). Other temperatures may also be of interest, depending on the design of the absorption assembly.

Upon cooling the ammoniacal solution, step d), after it has left the absorption assembly, the ammoniacal solution can be cooled to a temperature below the temperature of the ammoniacal solution in the first absorbent. The lower the temperature at which the ammonia solution cools, the more solids may precipitate. However, the required cooling energy also increases. If the ammonia solution is an aqueous solution under atmospheric pressure, the ammoniacal solution is preferably not cooled below 0 ° C (32 ° F). It has been found that it may be desirable to cool the ammoniacal solution to a temperature between about 0 ° C and 10 ° C (32 ° F and 50 ° F), especially at a temperature of about 5 ° C (41 ° F). Of course, other temperatures may also be of interest depending on the system design.

After the ammoniacal solution has left the separator the solution can be saturated essentially with carbon dioxide, but with reduced content or without solids. This solution is then heated to a temperature above the temperature at which it was previously cooled, thus making the ammoniacal solution less saturated or unsaturated with carbon dioxide. The more the solution is heated, the less saturated, or the more unsaturated, the ammoniacal solution. However, more heating also requires greater energy consumption. Also, a higher temperature of the ammonia solution also increases the ammonia depletion of the ammoniacal solution since the gaseous ammonia exits the ammoniacal solution. It has been found that the ammoniacal solution can conveniently, in the f) above, be heated to at least 7 ° C (45 ° F), such as between about 7 ° C and 15 ° C (45 ° F and 59 ° C). F), especially at between about 7 ° C and 10 ° C (45 ° F and 50 ° F). Of course, other temperatures may also be of interest depending on the system design.

The cooling and / or heating, respectively, of the ammoniacal solution can, for example, be carried out with heat exchangers. It has been found that it can be advantageous to at least partially carry out cooling and heating by the same heat exchanger, in which the ammoniacal solution leaving the absorption assembly in c) is the heating medium and the ammoniacal solution in the heat exchanger. leaving the separator in e) is the cooling medium. Thus, energy can be conserved. Using the cooled and separated ammonia solution as a cooling medium to cool the ammoniacal solution leaving the absorption assembly may not be sufficient to cool the ammoniacal solution that has left the absorption assembly, so it may be convenient to additionally use a medium of regular cooling, such as cold water. The regular cooling medium can be connected to the same heat exchanger as the separated ammonia solution, or to a separate heat exchanger. Thus, the ammonia solution leaving the absorption assembly can first be cooled by the ammoniacal solution of the separator and then further cooled by the regular cooling medium. Alternately, the ammoniacal solution is not used as a cooling or heating medium, but regular cooling and heating means are used instead.

The separator can be any type of separator capable of separating, and thus removing, solid particles or material from the ammonia solution. Depending on the requirements placed on the separator, it may be convenient to use a separator in the form of a hydrocyclone. A hydrocyclone can be an efficient way to remove solids from the ammonia solution. The slurry or slurry of the ammonia solution comprising solids is introduced to the hydrocyclone wherein the slurry or sludge is separated into an upper solution reduced in, or free of, solids and a low solids-rich flow. It has been found that it may be convenient with a solids content of the ammonia solution comprising solids that are introduced into the hydrocyclone of between about 5% and 10% by weight of the ammoniacal solution comprising solids entering the hydrocyclone. Ideally, essentially all solids are removed from the ammonia solution, giving a superior solution free of solids. It has been found that it may be convenient with a solids content of the higher solution between 0% and 1% by weight of the higher solution. The lower flow may also be allowed to contain a little liquid solution to facilitate the transport of solids in a liquid stream, so that a little of the ammonia solution can also be separated from the lower flow. The amount of liquid in the lower flow may be sufficient to transport the solids in a liquid stream but without reducing the concentration of carbon dioxide more than necessary to allow this transport. The lower flow can be a slurry or sludge, which leaves the ammonia solution.

Regardless of the type of separator used, it may be convenient that most or essentially all of the solids are removed from the ammonia solution to a slurry or sludge that exits, in whose slurry or sludge the amount of liquid has been balanced to allow transportation of the sludge. solids in a liquid stream but without reducing the concentration of carbon dioxide more than necessary to allow this transport. It may be convenient to have a solids content of at least 10% by weight of the suspension or sludge that exits, such as between approximately 10% and 20% by weight. weight of the suspension or mud that comes out.

According to another aspect, the object of the present invention is achieved by a carbon dioxide removal system for removing carbon dioxide from a process gas, the system comprising: an absorption assembly, said absorption assembly comprising at least a first absorbent, said first absorbent being configured to, within the first absorbent, allow contact between the process gas and an ammoniacal solution so that at least a part of the carbon dioxide of the process gas is captured by the ammoniacal solution; a first heat exchanger configured to cool the ammonia solution including captured carbon dioxide after it exited the absorption assembly; a separator configured to remove at least a portion of any solid in the cooled ammoniacal solution; a second heat exchanger configured to heat the ammonia solution after it has left the separator; and connection of pipes, and is configured to allow a flow, of the ammoniacal solution between the absorption assembly and the first heat exchanger, the first heat exchanger and the separator, the separator and the second heat exchanger, as well as the second heat exchanger and the absorption assembly.

It may be convenient to use the carbon dioxide removal system when carrying out the method discussed above.

It may be convenient to configure the first and second heat exchangers to cooperate with each other so that the ammoniacal solution which is cooled in the first heat exchanger is cooled at least partially by the ammoniacal solution which is heated in the second heat exchanger as the cooling medium, and the ammoniacal solution heated in the second heat exchanger is at least partially heated by the ammoniacal solution which is cooled in the first heat exchanger as a heating medium.

The previous discussion with reference to the method is in applicable parts also relevant to the system. Reference is made to that discussion.

BRIEF DESCRIPTION OF THE DRAWINGS The currently preferred embodiments will be discussed with reference to the drawings, in which: Figure 1 is a process flow diagram illustrating the steps of a method according to the present invention.

Figure 2 is a schematic front view of a carbon dioxide removal system in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES The process gas can be any type of process gas containing carbon dioxide, such as combustion gas from any combustion device such as furnaces, process heaters, incinerators, block boilers, and power plant boilers.

The ammonia solution can be any type of solution containing ammonia, such as a liquid solution, especially an aqueous solution. The ammonia in the ammonia solution can be in the form of ammonium ions and / or dissolved molecular ammonia.

C02 capture of the process gas by the ammonia solution can be achieved by the ammoniacal solution that absorbs or dissolves the C02 in any form, such as in the form of dissolved C02, carbonate or molecular bicarbonate.

The solids formed in the ammonia solution can be mainly ammonium carbonate and ammonium bicarbonate, especially ammonium bicarbonate.

The carbon dioxide removal system comprises tubing that connects the different parts of the system and is configured to allow ammonia solution and process gas, respectively, to flow through the system as required. The pipeline may include valves, pumps, nozzles, etc. as appropriate to control the flow of ammonia solution and process gas, respectively.

The absorbent or several absorbents of the absorption assembly may have any design that allows the ammoniacal solution to come into contact with the process gas. It may be convenient with an absorption design in the form of a column, where the ammonia solution flows from the top of the column to the bottom of the column and the process gas flows from the bottom of the column to the top of the column, so the solution and gas can be found and mixed together in the column, creating an inferium between the solution and the gas through which the carbon dioxide interface can be transported from the solution gas . The gas / solution contact can be increased, ie, the "interface" area can be increased, by using a packing in the column, thus improving the capture of carbon dioxide, the respective flows of the process gas and the ammonia solution inside, as well as the absorption assembly can be controlled by at least one pumping system and / or by the action of gravity.

If an absorbent is used in the form of a column, the process gas can enter the column through a pipe connected to the bottom of the column, transported up through the column and out of the column through a connected pipeline. to the top of the column, and the ammonia solution can enter through a pipe connected to the top of the column, transported down through the column by gravity and leave the column through a pipe connected to the bottom of the column. The ammonia solution and / or the process gas can additionally be recirculated in the column. If the ammoniacal solution is recirculated, the ammoniacal solution can alternatively be introduced into the column at the bottom of the column instead of at the top of the column, allowing a recirculation loop to transport the solution to the top of the column . The column can be associated with a pumping system to carry out the recirculation.

To be able to control the temperature of the column, a heat exchanger can be associated with the column. The heat exchanger, for example, can be part of a recirculation loop for the ammoniacal solution. Since the capture of carbon dioxide by the ammonia solution is an exothermic reaction, the heat exchanger can be used to cool the ammoniacal solution to maintain the interior of the absorbent at a desired and essentially constant temperature.

Depending on the design of and the demands on the absorption assembly, it may be convenient to use a plurality of absorbers to remove a desired amount of carbon dioxide from the process gas.

If a plurality of absorbers are used, they may have the same or different designs. The absorbers can be connected in series with each other to allow the process gas and / or ammonia solution to flow serially from one absorbent to another absorbent. However, it should be noted that the gas and the solution can flow in different directions among the absorbents connected in series. If, for example, an absorption assembly comprises three absorbers connected in series, denoted by x, y and z, the gas flow can be from the absorbent x to the absorbent and to the absorbent z, where the flow of the ammonia solution can be, for example, from the absorbent and the absorbent x to the absorbent zo in any other order.

With reference to Figure 1, a currently preferred method of agreement with the present invention will be described below.

In step 1, the ammonia solution in the form of an aqueous solution, as well as the process gas, enters the absorption assembly via pipes. The absorption assembly may comprise one or a plurality of absorbers, preferably in the form of packed columns.

In step 2, the ammonia solution, as well as the process gas, are introduced to the first absorbent column by separate pipes connected to said first absorbent column. The ammonia solution is introduced to the absorbent column by a pipe at the top of the column, after which the ammonia solution flows down through the packed column of the first absorbent. Simultaneously, the process gas is introduced to the first absorbent column by a pipe at the bottom of the column, after which the process gas flows up through the packed column of the first absorbent. The ammonia solution and the process gas meet in this way and come into contact with one another as they flow against the current in the first absorbent column. The packing of the column acts to increase the mixture and the area, contact interface, between the liquid phase and the gaseous phase in the column. The carbon dioxide of the process gas is transported from the gas phase to the liquid phase and thus captured by the ammoniacal solution. The ammonia solution and / or the process gas can be recirculated in the absorbent. Thus, the ammonia solution can exit the absorbent by means of a pipe at the bottom of the absorbent column and be pumped back to the top of the absorbent to reintroduce it to the absorbent. During this recirculation outside the absorber, the temperature of the ammonia solution can also be adjusted by a heat exchanger.

It should be noted that the ammonia solution and / or the process gas can having already passed through one or more absorbers after entering the absorption assembly before entering said first absorbent, depending on the design of the system.

In step 3, the ammoniacal solution leaves the first absorbent as well as the absorption assembly via a pipe.

In step 4, the ammonia solution is introduced into at least one heat exchanger and cooled. As a result of cooling, a part of the captured carbon dioxide is precipitated as salt. It may be preferred to employ two separate heat exchangers, the first being used using cooled ammoniacal solution as the cooling medium and the second using cold water as a cooling medium.

In step 5, the cooled ammoniacal solution including salt solids is introduced to a hydrocyclone. In the hydrocyclone, the ammonia solution is separated into a solid rich lower stream and an upper solution with less than 1% by solids weight. Thus, most of the solids have been removed from the ammonia solution by the hydrocyclone. The lower solid-rich flow can be transferred to a regenerator where it is subjected to increased temperature and pressure to remove the captured carbon dioxide in the form of a stream leaving high-purity carbon dioxide gas. The ammoniacal solution thus regenerated from the lower flow can be allowed to be reintroduced to the carbon dioxide removal system to capture more carbon dioxide.

In step 6, the ammonia solution, that is, the upper hydrocyclone solution, is reheated. To save energy, the reheating can preferably be carried out by the same first heat exchanger as discussed under step 4, with the ammoniacal solution cooled in step 4 as the heating medium. If required, an additional heat exchanger can also be used with a traditional heating medium, such as warm water. By heating the ammonia solution, the solution becomes unsaturated with respect to carbon dioxide, allowing it to capture more carbon dioxide without inducing any precipitation.

In step 7, the reheated ammonia solution is reintroduced to the absorption assembly to capture more carbon dioxide from the process gas, either in the first absorbent column or in a different absorbent if a plurality of absorbers are comprised in the absorption assembly .

It should be noted that the method can be continuous. Thus, all the previous stages can occur concurrently involving different parts of the ammonia solution.

With reference to Figure 2, a preferred carbon dioxide removal system 10 according to the present invention, configured to carry out a currently preferred method according to the present invention, will be described below. In Figure 2, the pipe is represented by arrows for easier understanding.

The carbon dioxide removal system 10 comprises an absorption assembly 12, said absorption assembly 12 comprising three absorption columns, a first absorption column 14, a second absorption column 16 and a third absorption column 18. The first The absorption column comprises a lower packed bed 14a and a lower packed bed 14b.

A process gas inlet pipe of the first absorption column 30 is connected to the lower part of the first absorption column 14 to allow the process gas including carbon dioxide of for example, a power plant to be introduced to the first absorption column 14. A process gas outlet pipe of the first absorption column 32, is connected to the upper part of the first absorption column 14 to allow the process gas to exit the column 14 towards the third column 18 after having traveled through column 14 from the bottom to the top.

A first recirculation loop of the first absorption column 20 is connected to the first absorption column 14, allowing the ammonia solution to flow through the pipe from the bottom of the absorption column 14 to the top of the column 14. A pump 22 is comprised in loop 20 to effect circulation of the ammonia solution. Also, a heat exchanger 24 is comprised in loop 20 to control the temperature of the ammonia solution.

An ammonia solution outlet pipe of the first absorption column 26 is configured to drive the ammonia solution away from the bottom of the first absorption column 14 to the hydrocyclone 34. The outlet pipe 26 comprises an outlet pump 28 for control the outflow of the ammonia solution from the first absorption column 14.

An ammonia solution inlet pipe of the first absorption column 36 is configured to allow the ammonia solution to flow from the third column 18 to the bottom of the first column 14, where it is allowed to mix with, and recirculate with , the ammoniacal solution recirculated in the first column 14 by means of the recirculation loop 20.

An ammonia solution inlet pipe of the second absorption column 38 is configured to allow the ammonia solution to flow from the hydrocyclone 34 to the bottom of the second column 16, where it is allowed to mix with, and recirculate with, the ammoniacal solution recirculating in the second column 16 by means of a recirculation loop 40 associated with the column 16.

The recirculation loop of the second column 40 is connected to the second absorption column 16, allowing the ammonia solution to flow through the pipe from the bottom of the absorption column 16 to the top of the column 16. A pump 42 is comprised in the loop 40 to effect the circulation of the ammoniacal solution Also, a heat exchanger 44 is comprised in loop 40 to control the temperature of the ammonia solution.

Connected to the recirculation loop of the second absorption column 40 is an ammonia solution inlet pipe of the third column 46 configured to allow the flow of the ammonia solution from the recirculation loop 40 to the bottom of the third column 18 where the allows it to be mixed with, and recirculated with, the ammoniacal solution that is recirculated in the third column 18 by a recirculation loop 48 associated with the column 18. The flows through the pipe 46 and the recirculation loop 40, respectively, they are controlled by valves (not shown) included in pipe 46 and loop 40.

The recirculation loop of the third absorption column 48 is connected to the third absorption column 18, allowing the ammonia solution to flow through the pipe from the bottom of the absorption column 18 to the top of the column 18. A pump 50 is comprised in the loop 48 to effect the circulation of the ammonia solution. Also, a heat exchanger 62 is comprised in loop 48 to control the temperature of the ammonia solution.

The lower part of the third column is also connected to a supply of poor ammonia solution via the poor feed pipe 52. The lean ammonia solution, for example from the regeneration process, can then be fed into the lower part of the third column 18 by the pipe 52 where the lean solution is allowed to mix with, and recirculate with, the ammoniacal solution which is recirculated in the third column 18 by means of the recirculation loop 48 as well as with the ammoniacal solution fed into the lower part of the column 18 by pipe 46 from second column 16.

Connected to the recirculation loop of the third absorption column 48 is the ammonia solution inlet pipe of the first column 36 configured to allow the flow of the ammonia solution from the recirculation loop 48 to the bottom of the first column 14 in where it is allowed to mix with, and recirculate with, the ammoniacal solution which is recirculated in the first column 14 by the recirculation loop 20 associated with the column 14. The flows through the pipe 36 and the recirculation loop 48, respectively, they are controlled by valves (not shown) that are included in pipe 36 and loop 48.

The process gas outlet pipe of the first absorption column 32 is connected to the bottom of the third column 18, allowing the gas to enter the column 18 and flow upwards through the column 18. While the gas process reaches the top of the column 18, can be introduced to the second column 16 through the bottom of said second column 16, the second column 16 is configured on the third column 18, by pipe (not shown) connecting the upper part of the column 18 with the lower part of the column 16. The clean process gas of carbon dioxide can leave the second column 16 by means of the gas outlet 60 connected to the upper part of the column 16.

The ammonia solution outlet pipe of the first absorption column 26, connected to the bottom of the first column 14, allows the ammoniacal solution rich in carbon dioxide to come into countercurrent contact with the process gas rich in dioxide carbon of the first column 14 to exit the first column 14 as well as exit the absorption assembly 12. The outlet pipe 26 is connected to a first thermal exchanger 54, external to the absorption assembly 12, in which the solution The ammoniacal heat exchanger 54 of the first column 14 can be cooled by heat exchange with the colder ammoniacal solution of the hydrocyclone 34.

The first heat exchanger 54 is connected to a second heat exchanger 56 connected to a cold water source 58, in which second heat exchanger 56, the ammonia solution can be further cooled by heat exchange with cold water from the cold water source 58.

The second heat exchanger 56 is connected to the hydrocyclone 34, allowing the ammoniacal solution, including any precipitated solid, to be introduced to the hydrocyclone 34 in which the ammoniacal solution is separated into a solid rich feed, the lower flow, and a saturated solution essentially free of solids. The lower flow can be eliminated from the system 10 by the outlet pipe 64 a, for example, a regenerator (not shown).

The hydrocyclone 34 is connected to. first heat exchanger 54 to allow the upper solution to be heated by heat exchange with the hottest ammoniacal solution leaving the first column 14.

The first heat exchanger 54 is connected to the second column 16 by the inlet pipe 38, allowing the ammoniacal solution to be reintroduced to the absorption assembly 12.

Example With reference to Figure 2, a specific preferred embodiment will be described by way of example.

The combustion gas that comes from a desulfurization system of wet combustion gas from a power plant is cooled in the existing processing equipment before entering the system for the elimination of carbon dioxide 10 and the absorption assembly 12. While the combustion gas saturated with water cools, the water condenses. This combustion gas is compressed and cooled further to 15 ° C (59 ° F), ie to the temperature of the first absorption column 14.

The combustion gas is introduced to the first absorption column 14, passes upwards through the packed column and makes countercurrent contact with the ammoniacal absorption solution. C02 is captured by the ammoniacal solution. Approximately 70 percent of the carbon dioxide captured by the system 10 is captured in the first column 14. The first absorbent operates at approximately 15 ° C (59 ° F) to take advantage of the increased reaction rate of this relatively high temperature. This high operating temperature also prevents the production of solids in the packed column. The flow rate of the ammonia solution of the third absorbent 18 to the first absorbent 14 is matched to the flow rate of the poor feed solution of the third absorbent. The heat of reaction is removed from column 14 by passing the ammoniacal solution through a cold water cooled heat exchanger 24 located in the circulation loop 20.

The ammonia solution is pumped from the third absorption column 18 to the first absorption column 14. During circulation in the first absorption column 14, the solution increases the CO 2 content by the capture of the combustion gas. The C02 content of the ammonia solution increases to the saturation concentration but does not precipitate solids due to the relatively high operating temperature.

The combustion gas is now introduced into the third absorption column 18. The combustion gas passes upwards from the packed column 18 and makes contact with the poor ammoniacal solution introduced in the third column 18 countercurrent. The heat of the reaction is removed by circulating the solution through a heat exchanger cooled by cold water in the circulation loop 48. The poor solution of the regeneration process is introduced into the lower part of the column 18 to be mixed with the solution of inventory that is already present. This does not require a high head pump since the change in elevation is small (the feed tank of poor solution is located on the ground, as well as the lower part of the third absorbent 18). The flow is limited depending on the flow rate of combustion gas that is processed. The additional ammonia solution discharged from the second absorption column 16 is also introduced into the third absorption column 18. Approximately 20 percent of the captured C02 is captured in the third absorption column 18.

The solution is circulated in the third absorber 18 to capture CO 2 from the combustion gas passing therethrough. Solids do not occur at this stage of the absorption process. The third absorber 18 operates at a temperature of 10 ° C (50 ° F) to improve the C02 capture of the combustion gas stream that has already had most of the C02 removed. Solids are not produced because the solution circulating is relatively poor (not saturated with C02 products).

The combustion gas is then introduced into the second absorption column 16. The combustion gas passes upwards through the packed bed to make countercurrent contact with the ammoniacal solution circulating through the loop 40. it is operated at a lower temperature, about 7 ° C (45 ° F) to help capture ammonia vapors lost from the previous absorption columns 14 and 18 to the combustion gas. A little C02 (approximately 10 percent of the total captured) is also captured in the second absorption column 16. The heat of reaction is removed by circulating the absorption solution through a heat exchanger cooled with cold water 44.

The ammoniacal solution transferred to the second absorption column 16 is saturated with dissolved C02 (ammonium bicarbonate) while leaving the hydrocyclone. The temperature of the absorption solution is partially increased by means of the heat exchanger 54 to desaturate the ammoniacal absorption solution and to prevent the formation of solids in the second absorption column 16. Part of the temperature increase is achieved by thermal exchange. The rest of the temperature increase is due to the heat of reaction in the second absorption column.

The ammoniacal absorption solution coming from the second absorption column 16 is pumped to the third absorption column 18. In the third absorption column 18, the solution of the second column 16 is mixed with the incoming poor solution of the regenerator and the inventory of existing solution. At this point the process starts again, forming a circulation loop.

Compounds C02 (ammonium bicarbonate) are removed from the solution contained in the first absorption column 14 in the following manner: The solution is pumped by the pump 28 from the first absorption column 14 and is introduced to a heat exchanger 54. provides cooling for the heat exchanger by the free solid solids solution returning from the hydrocyclone 34. The solution then passes through a second heat exchanger 56 to cool the solution sufficiently for significant amounts of solids to precipitate out of the solution. The cooling for the second heat exchanger 56 is provided by cold water. Heat exchanger 54 reduces the temperature of the solution to 13 ° C (55 ° F). In the process of cooling the solution, the solubility limit of the ammonium bicarbonate is reached and the solids begin to precipitate.

The solution with solids then flows to the second heat exchanger 56 which is cooled by cold water. This heat exchanger 56 cools the solution and the solids to 5 ° C (41 ° F) to complete the precipitation of solids from the solution. Part of the heat load of the second heat exchanger is the heat of crystallization of the ammonium bicarbonate solids. The rich saturated solution will release solids of ammonium bicarbonate at a rate that corresponds to the C02 capture rate of the absorbers. The solids in the sludge can reach approximately 10 percent by weight at this point.

The. Heat load of this second heat exchanger 56 is high during process firing. After the process is in operation, the only heating work of this exchanger 56 is the relatively small amount of cooling required to lower the temperature of the process solution from about 13 ° C (56 ° F) to 5 ° C ( 41 ° F). This heat load actually cools the rich mud feed stream and includes the heat load of crystallizing the bicarbonate of ammonium solids out of the solution.

The sludge produced in the heat exchangers 54 and 56 is then directed to the hydrocyclone 34 for removal of solids. Hydrocyclone 34 essentially removes all solids together with a little of the liquid ammonia solution. Sufficient liquid is removed with the solids to prevent pipeline clogging and downstream control equipment.

The lower sludge flow is sent to a feed storage tank to be fed to the regenerator. The liquid level in the feed tank will be controlled by balancing the sludge inlet flow rate with the feed (sludge) outflow to the regenerator.

The upper solution essentially free of solids (less than 1% solids) is transferred back to the first heat exchanger 54 where it is used to cool the saturated solution coming from the first absorption column 14. The solids-free solution is heated at the same time at approximately 7 ° C (45 ° F). Any difference in temperature required for process control is corrected by adjusting the refrigerant flow to the other heat exchangers of the absorbent process 24, 44 and 62.

The solids-free solution is then directed to the second absorption column 16 to continue the absorption process. In the second adsorber 16, the solution is mixed with the column inventory and used to capture ammonia from the flue gas flowing from the third adsorbent 18. The high concentration of ammonia in the third adsorbent 18 results in high losses of ammonia from the combustion gas flowing to the second absorber 16. A little C02 is also captured in the second absorber (approximately 10 percent of the total C02 captured).

It should be noted that cooling the ammonia solution before entry to hydrocyclone 34 does not increase the cooling load of the process since otherwise the cooling would have had to increase in the recirculation loops due to the exothermic reactions that take place in the absorbent.

Solid ammonium bicarbonate is not present in the absorbent. This allows the use of packaging materials that are sensitive to the presence of solids but provides excellent mass transfer. Pumps that provide circulation are never affected by the presence of solids. The seals of the pump are also not affected by the presence of solids.

The ammonium bicarbonate is precipitated out of solution in the heat exchangers 54 and 56 outside the absorption assembly 12. These heat exchangers are outside the absorption process and are manufactured in such a way that they are not adversely affected by the presence of solid The ammonia solution that is free of solids after leaving the hydrocyclone is reheated by exchange in the heat exchanger 54 to recover the refrigerant that was used to cause the precipitation. This stage saves the cost of any cooling that can be recovered, thus reducing the loss of energy in the entire process.

The solution sent to the second absorbent 16 for capturing ammonia does not contain solids so that the deposition of solids in the absorbent does not occur. The temperature of the returning solution is above the saturation temperature of carbon dioxide so that additional ammonium bicarbonate can be produced without allowing any deposition of solids.

The solution coming from the second absorbent 16 is directed to the third absorbent 18 to mix with the incoming poor solution to resume the C02 capture process. This destination prevents the accumulation of solids in the solution that is shown to have harmful effects.

While increasing the percentage by weight of solids from the feed of sludge to the generator, the heat per unit mass of the product of C02 produced decreases. The reason for this is the reduction of significant heating required for the liquid that accompanies the sludge in high percentages by weight against the relatively large amount of liquid accompanying the solids in a sludge with a low percentage of solids weight.

The cost of the entire process equipment is reduced by giving a correct size to the heat exchangers so that the absorbent columns only remove the heat required to maintain the process conditions. Some heat of reaction and most of the combustion gas cooling required by the process are removed by adding a cold solution of the upper hydrocyclone back to the absorbents While the invention has been described with reference to a number of preferred embodiments, it will be understood by those skilled in the art that various changes can be made and equivalents can be replaced by elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention is not limited by the particular embodiments described as the best mode heretofore contemplated to carry out this invention, but that the invention will include all modalities that are within the scope of the appended claims. Furthermore, the use of the terms first, second, etc., do not denote any order of importance or chronology, but the terms first, second, etc., are used to distinguish one element from another.

Claims

CLAIMS 1 . A method for removing carbon dioxide from a process gas, the method characterized in that it comprises a) allowing an ammoniacal solution to be introduced into an absorption assembly, said absorption assembly (comprising at least one first absorber operating at a temperature between about 10 to 20 ° C (50 to 68 ° F) b) contacting the ammonia solution with the process gas in the first absorber, the ammonia solution captures at least a part of the carbon dioxide from the process gas; c) allow the ammoniacal solution to exit the absorption assembly after the capture of carbon dioxide; d) cooling the ammonia solution, at a temperature between about 0 to 10 ° C (32 ° to 50 ° F) outside the absorption assembly, wherein at least a part of the captured carbon dioxide is precipitated as a solid salt; e) allowing the cooled ammoniacal solution to be introduced to a separator, in which separator at least a portion of the precipitated solids are removed from the ammoniacal solution, after which the ammoniacal solution is allowed to exit the separator; f) heating the ammonia solution; and g) allowing the heated ammonia solution to be reintroduced into the absorption assembly. 2. The method according to claim 1, characterized in that the temperature of the ammonia solution in b) is between about 10 and 20 ° C (50 and 68 ° F). 3. The method according to claim 2, characterized in that the temperature of the ammonia solution in b) is about 15 ° C (59 ° F). 4. The method according to claim 1, characterized in that the ammoniacal solution in d) is cooled to approximately 5 ° C (41 ° F). 5. The method according to claim 1, characterized because the ammonia solution in f) is heated to at least 7 ° C (45 ° F). 6. The method according to claim 1, characterized in that the ammoniacal solution in f) is heated to between about 7 and 15 ° C (45 and 59 ° C). 7. The method according to claim 1, characterized in that the ammoniacal solution in f) is heated to between about 7 and 10 ° C (45 and 50 ° C). 8. The method according to claim 1, characterized in that the cooling of d) and the heating of f) is achieved at least partially by a heat exchanger, in whose heat exchanger the ammoniacal solution leaving the absorption assembly in c) is the heating medium and the ammoniacal solution leaving the separator in e) is the cooling medium. 9. The method according to claim 1, characterized in that the cooling of d) is achieved at least partially by means of a heat exchanger, in which heat exchanger cold water is used as a cooling medium. 10. The method according to claim 1, characterized in that the separator is a hydrocyclone. eleven . The method according to claim 1, characterized in that a little liquid solution is also removed together with the solids in the separator, forming an outlet sludge, whose slurry or sludge has a solids content between about 10% and 20% by weight of the suspension or sludge. 12. The method according to claim 1, characterized in that it further comprises: h) contacting the hot ammonia solution with the process gas in a second absorber of the absorption assembly, the second absorbent is separated from the first absorbent, the ammoniacal solution absorbs and dissolves at least a part of the carbon dioxide of the process gas in the second absorbent. 13. A carbon dioxide removal system for removing carbon dioxide from a process gas, the system characterized by an absorption assembly, comprising at least a first absorbent, said first absorbent being configured to, within the first absorbent, allow contact between the process gas and an ammoniacal solution in such a way that at least a part of the carbon dioxide of the process gas is captured by the ammoniacal solution; a first heat exchanger configured to cool the ammonia solution including captured carbon dioxide after it has left the absorption assembly; a separator configured to remove at least a portion of any solid in the cooled ammonia solution after it has left the first heat exchanger; a second heat exchanger configured to heat the ammonia solution after it has left the separator; and tubing connected and configured to allow a flow of the ammonia solution between, the absorption assembly and the first heat exchanger, the first heat exchanger and the separator, the separator and the second heat exchanger, as well as the second heat exchanger and the assembly of absorption. 14. The system according to claim 13, characterized in that the first and second heat exchangers are configured to cooperate with each other so that the ammoniacal solution which is cooled in the first heat exchanger is at least partially cooled by the ammoniacal solution which is heated in the second heat exchanger as cooling medium, and the ammoniacal solution which is heated in the second heat exchanger is at least partially heated by the ammoniacal solution which is cooled in the first heat exchanger as a medium. heating.